Ultra-high frequency oscillator tubes



Feb. 21, 1961 D. CHARLES EI'AL 2,972,700

ULTRA-HIGH FREQUENCY OSCILLATOR TUBES Filed April 19, 1955 2Sheets-Sheet 1 Fig.1.

Fig.2.

Feb. 21, 1961 D. CHARLES ETAL ULTRA-HIGH FREQUENCY OSCILLATOR TUBES 2Sheets-Sheet 2 Filed April 19, 1955 ULTRA-HIGH FREQUENCY OSCILLATORTUBES Daniel Charles and Oscar Dohler, Paris, France, assignors toCompagnie Generale de Telegraphic Sans Fil, a corporation of FranceFiled Apr. 19, 1955, Set. No. 502,267 Claims priority, applicationFrance Apr. 27, 1954 15 Claims. (Cl. SIS-3.6)

The present invention relates to high frequency oscillators, and moreparticularly to centimetric and millimetric wave oscillators.

Oscillators are already known in which the oscillations are produced bythe interaction between one or more electron beams and the field of ageometrically periodical line in which the ultra-high frequency wavesare generated.

It is sometimes difficult to construct a delay line capable ofpropagating ultra-high frequency waves in a given frequency band. Inparticular, when the wavelength is in the millimetric band, it becomesincreasingly difiicult to construct the delay line with a sufiicientprecision; the slightest irregularity in its configuration, for example,in its geometrical periodicity, may sufiice to make the line unable topropagate the ultra-high frequency waves in the desired band, whichmakes the oscillator unable to operate.

It is an object of the present invention to provide a new oscillator inwhich oscillations are obtained by means of a periodical structureunable to propagate ultra-high frequency waves along its length, i.e. astructure offering an infinite impedance to the propagation therealongof ultrahigh frequency waves, which accordingly does not require thehigh degree of accuracy necessary in traveling wave oscillators and istherefore easier to manufacture.

The oscillator tube in accordance with the invention comprises twoelectron emissive sources positioned to propagate two parallel beams inopposite directions. These beams are separated along their length by ageometrically periodical structure along which electromagnetic waves areincapable of being propagated in the operating frequency band of thetube, i.e., a structure ofiering an infinite impedance to thepropagation therealong of ultra-high frequency waves in the operatingband of this tube. Such a structure may, for instance, be a ladder lineof the type shown by Pierce in his book Traveling Wave Tubes, VanNostrand, New York 1950, in Figs. 5, 7, page 90. It may also consist ofa grid with square, circular or polygonal meshes. As will be shownhereinafter, in operation, the two beams of this tube interact with eachother thereby converting the direct current energy applied to the tubeinto ultra-high frequency oscillations.

The invention will be better understood from the following descriptionwith reference to the attached drawings wherein:

Fig. 1 shows in longitudinal section one embodiment of the tube inaccordance with the invention;

accordance with the invention.

The tube shown in Fig. 1 comprises, within a cylindrical evacuatedenvelope 12, a cathode 8 at one end thereof,

.and an annular cathode 9 at the opposite end. These two States Patentcathodes which are substantially coaxial with the envelope 12 emit,respectively in opposite directions, two coaxial 2,912,100 Patented Feb.21, 1961 beams 1 and 2. Beam 2 is cylindrical and beam 1 is tubular. Theelectrons of these beams are respectively captured at the end of theirpaths by collectors 10 and 11, the latter being annular in form. Thebeams are separated by a cylindrical structure 3, shown in longitudinaland transverse sections respectively in Figs. 2 and 3. This structureconsists of a series of wires coiled in parallel rings 18, separated bygaps 16 and supported by metal mountings 17 to which these rings areintegrally connected. This type of line is known as ladder type line andforms in fact a grid. It is known that in such a geometricallyperiodical structure electromagnetic waves are not propagated, as shownfor instance by Pierce (see above). At both ends of structure 3 arerespectively arranged two delay line sections 6 and 7, for instance,intended only for coupling the two beams 1 and 2 to the output circuitsrespectively in the desired frequency band. The ends of these sectionsin the neighborhood of structure 3 are provided with attenuators 4 and5, to absorb without reflection any energy that might be propagated inthose sections toward these attenuators, for instance, because of amismatch between the output and a load connected thereto. Theseattenuators may for instance be constituted by a dissipative substancesuch as aquadag covering the ends of the sections 6 and 7. The otherends of the latter are coupled, in the neighborhood of the cathodes, tothe respective outputs 14 and 15 which may be joined together by meansof a connection 30 shown diagrammatically inside the tube.

It is assumed, for instance that collectors 10 and 11 and delay lines 6and 7 are grounded and the cathodes 8 and 9 are raised by a source 19 toa negative potential which can be adjusted by means of the tap 21. Thestructure 3 is brought to a positive potential with respect to thecathodes 8 and 9 by means of a source 20, provided for instance with apotentiometer 13 having a variable .tap 22.

In operation, by suitably adjusting the respective velocities of thebeams 1 and 2, ultra-high frequency oscillations are provided at theoutputs 14 and 15.

The adjustment of the beam velocities is performed by adjustingthepositive potential of the structure 3, whereby both beams 1 and 2 willhave substantially the same velocity.

The operation of this device according to the invention may be explainedin the following way, although applicant does not wish to be bound byany theoretical explanation.

Supposing one of beamsl and 2 is initially density modulated, then thehigh frequency electric field of the space charge due to this beampenetrates through period- 'ically spaced apertures in the structure 3and interacts with the second beam, thereby velocity modulating theelectron flow thereof. Since this second beam propagates in a directionopposite to the first beam and at uniform velocity, this velocitymodulation takes place at a series of periodically spaced points in thebeam. As the second beam progresses, the velocity modulation transformsitself into density modulation, thereby creating a high frequencyelectric field of the space charge due to the second beam. This highfrequency electric field reciprocally penetrates through apertures ofthe structure 3 and interacts with the first beam, thereby creating inthe flow thereof velocity modulation at a series of periodically spacedpoints. Since this velocity modulation transforms itself into densitymodulation of the first beam, it may be readily seen that there isreciprocal feedback interaction between both beams through theseapertures of the periodic structure, whereby density'modulations areamplified and oscillations are able to start up, if the beam currentsare sufficiently high. The initial density modulation may be due to thenoise inherently present in the beams. As

Designating the frequency of the output oscillations by f and the pitchof the structure 3 by p, it may be the- .oretically stated that assumingthe velocities of both me. 5. p

If V=2,500 volts and 2p=0.04 cm., the output frequency 7 will be of75,000 mc./s., i.e., the wavelength of the output energy will be '4 mm.which shows that the oscillator is well suited to be used as amillimeter wave oscillator. The voltage V may be regulated by means ofthe potentiometer 13. I

It may be easily shown that if the beam 1 has a velocity v and beam 2 avelocity v the output frequency is equal to beams being equal:

1 1.1 2 p( i+ z) Of course, more than two beams having same or difierentvelocities could be used.

Another embodiment of the invention is shown in Figs. 4 and 5. In thistube the beams 31 and 32 are propagated in a direction normal to anelectric and magnetic field which are perpendicular to each other.

In the embodiment shown, the tube comprises a metallic envelope 33 whoselateral walls are joined by metallic bars 34 forming a ladder type delayline 35. Parallel to this line are located two smooth electrodes 36 and37, respectively on opposite sides of the line 35. They bound with thelatter two interaction spaces where beams 31 and 32 are respectivelypropagated from two guns 38 and 39 respectively located at the oppositeends of the tube substantially at the same level as electrodes 36 and 37respectively. The latter are negatively biassed with respect to thestructure 35 which is grounded, by means of sources 40 and 41respectively, and are made .slightly positive with respect to therespective cathodes of the guns 38 and 39 by means of sources 42 and 43respectively. A magnetic field, normal to the beam propagation directionand to the electric field set up by the sources 42 and 4-3, is providedin the interaction spaces by means of polar pieces 4 and 45 which may beseen in Fig. 5.

The electrons of the beams are respectively collected at the end oftheir travel by collectors 46 and 47.

It should be noted that the structure and the relative location of theelectrodes 36 and 37 of the electron guns 38 or 39, and of the polarpieces 44 and 45, are entireIy similar to those encountered in anytravelling wave tube of the magnetron type.

At the end of their respective paths, the beams 31 and 32 pass throughdelay line portions 48 and 49, which, in the embodiment shown, are flathelices whose ends remote from the adjacent collector are covered withan absorbing material as in the case of Fig. 1. As in this latter case,they serve to couple the beams to the outputs S and 51 respectively.

The velocity of the beams may be adjusted for instance by means of theadjustable taps 52 and 53, or by adjusting the intensity of the magneticfield.

The operation of the tube is the same as in the casev of Fig. 1.

It will be appreciated that many variations, obvious to those skilled inthe art, may evidently be considered without departing from the scope ofthe invention. In particular, the tube of Fig. 4- could be of circularshape instead of being of straight shape.

We claim:

1. A microwave oscillator tube for a given frequency band, comprisingwithin an evacuated envelope: a geometrically periodical electricallyconductive structure, having periodically spaced apertures, two ends andtwo sides, and offering an infinite impedance to the propagationtherealong of electromagnetic waves in at least said given frequencyband; two electron sources each positioned at one end and respectivelyon opposite sides of said structure, to emit respectively in oppositedirections two electron beams parallel to said structure and effectivelyentering into mutual interaction only through said periodically spacedapertures of said structure; two collectors each positioned at one endandrespectively on opposite sides of said structure to collectrespectively the electrons of said beams; means for controlling thevelocity of said beams; output means at least at one end of saidstructure; and coupling means for coupling in said predeterminedfrequency band the electromagnetic field of at least one of said beamsto said output means.

2. A microwave oscillator tube for a given frequency band, comprisingWithin an evacuated envelope: a geometrically periodical electricallyconductive structure, having periodically spaced apertures, two ends andtwo sides, and offering an infinite impedance to the propaga tiontherealong of electromagnetic waves in at least said given frequencyband; two electron sources each positioned at one end and respectivelyon opposite sides of said structure, to emit respectively in oppositedirections two electron beams parallel to said structure and effectivelyentering into mutual interaction only through said periodically spacedapertures of said structure; two collectors each positioned at one endand respectively on opposite sides of said structure to collectrespectively the electrons of said beams; means for bringing saidstructure to a predetermined direct current potential; output means atleast at one end of said structure; and coupling means for coupling insaid predetermined frequency band the electromagnetic field of at leastone of said beams to said output means.

3. A microwave oscillator tube for a given frequency band, comprisingwithin an evacuated envelope: a geometrically periodical electricallyconductive structure, having periodically spaced apertures, two ends andtwo sides, and offering an infinite impedance to the propagationtherealong of electromagnetic waves in at least said given frequencyband; two electron sources each positioned at one end and respectivelyon opposite sides of said structure, to emit respectively in oppositedirections two electron beams parallel to said structure and effectivelyentering into mutual interaction only through said periodically spacedapertures of said structure; two collectors each at one end andrespectively on opposite sides of said structure to collect respectivelythe electrons of said beams; means for controlling the velocity of saidbeams; output means at least at one end of said structure; and at leastone delay line section adjacent one of said collectors and in coupledrelationship with at least one beam and with said output in saidpredetermined frequency band.

4. A microwave oscillator tube for a given frequency band, comprisingwithin an evacuated envelope: a geometrically periodical electricallyconductive structure, having periodically spaced apertures, two ends andtwo sides, and ofiering an infinite impedance to the propagationtherealong of electromagnetic waves in at least said given frequencyband; two electron sources each positioned at one end and respectivelyon opposite sides of said structure, to emit respectively in oppositedirections two electron beams parallel to said structure and effectivelyentering into mutual interaction only through said periodically spacedapertures of said structure; two collectors each positioned at one endand respectively on opposite sides of said structure to collectrespectively the electrons of said beams; means for controlling the-velocity of said beams; two outputs each positioned at one end of saidstructure; and two delay line portions respectively adjacent saidcollectors and respectively in coupled relationship with at least one ofsaid beams and said outputs in said predetermined frequency band.

, 5. A microwave oscillator tube for a given frequency band, comprisingwithin an evacuated envelope: a geometrically periodical electricallyconductive structure, having periodically spaced apertures, two ends andtwo sides, and olfering an infinite impedance to the propagationtherealong of electromagnetic waves in at least said given frequencyband; two electron sources each positioned at one end and respectivelyon opposite sides of said structure, to emit respectively in oppositedirections two electron beams parallel to said structure and effectivelyentering into mutual interaction only through said periodically spacedapertures of said structure; 'two collectors each positioned at one endand respectively on opposite sides of said structure to collectrespectively the electrons of said beams; two elongated electrodesparallel to said structure and defining therewith two interactionspaces; means for providing in said interaction spaces an electric fieldand a magnetic field normal to each other and to the propagationdirection of said beams; two outputs each positioned at one end of saidstructure; and two delay line portions respectively adjacent saidcollectors and in respective coupled relationship with said beams andsaid outputs in said predetermined frequency band.

6. A microwave oscillator tube for a given frequency band, comprisingmeans forming a geometrically periodical structure essentiallypreventing propagation therealong of electromagnetic waves in at leastsaid given frequency band and provided with aperture means, means forpropagating two electron beams in opposite directions with respect toeach other and exclusively on opposite sides of said first-mentionedmeans to generate oscillatory electromagnetic energy by the effectivemutual interaction of said two beams through said aperture means, andoutput means for extracting said oscillatory electromagnetic energy fromsaid tube.

7. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a given frequency band, comprising means forproducing a plurality of electron beams having velocity components inmutually opposite directions and propagating to provide an area ofoverlap in the direction of said components, means including ageometrically periodical structure located within said area of overlapand essentially preventing propagation therealong of electromagneticwaves within at least said given frequency band for generatingoscillatory electromagnetic energy by the mutual interaction of theeffects of 'said beams within said area of overlap, and output means forextracting said oscillatory energy from said tube.

8. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a given frequency band and provided withmeans forming a geometrically periodical structure essentiallyinoperative to enable the propagation therealong of electromagneticenergy within at least said given frequency band, comprising cathodemeans operative to emit electrons adapted to flow in a plurality ofpaths along at least a portion of said geometrically periodicalstructure, means including said portion of said geometrically periodicalstructure for generating oscillatory electromagnetic energy within saidtube by the indirect interaction of the electron flow in said paths inrelation to said geometrically periodical lap in the region of saidportion of said geometrically periodical structure in the direction ofsaid components, and output means for extracting said oscillatoryelectromagnetic wave energy from said tube.

9. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a. given frequency band, comprising meansfor producing a plurality of electron beams having velocity componentsin mutually opposite directions and propagating to provide an area ofoverlap in the directionof said components, means including ageometrically periodical structure having means essentially preventingpropagation therealong of electromagnetic waves within at least saidgiven frequency band and located within said area of overlap betweenbeams having velocity components in said opposite directions forgenerating oscillatory electromagnetic energy by the mutual interactionof the electric fields of said beams within said area of overlap, andoutput means for extracting said oscillatory energy from said tube.

10. A microwave discharge system according to claim 9 'wherein saidgeometrically periodic structure is provided with a plurality of spacedapertures.

11. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a given frequency band, comprising means forproducing two electron beams having velocity components in mutuallyopposite directions and propagating to provide an area of overlap in thedirection of said components, means including a geometrically periodicalstructure essentially preventing propagation therealong ofelectromagnetic waves within at least said given frequency band andlocated intermediate said two beams for generating oscillatoryelectromagnetic energy by the mutual interaction of the effects of said.beams through said geometrically periodic structure within said area ofoverlap, and output means for extracting said oscillatory energy fromsaid tube.

12. A microwave discharge system according to claim 11, wherein each ofsaid beams is of substantial width.

13. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a given frequency band and provided withmeans forming a geometrically periodical structure essentiallyinoperative to enable the propagation therealong of electromagneticenergy within at least said given frequency band, comprising cathodemeans operative to emit electrons adapted to 'fiow in a plurality ofpaths along at least a portion of said geometrically periodicalstructure and on opposite sides thereof, means including said portion ofsaid geometrically periodical structure for generating oscillatoryelectromagnetic energy within said tube by the mutual interaction of theelectron flow in said paths in relation to said geometrically periodicalstructure including means for producing electron flow in said pathshaving velocity components in essentially mutually opposite directionsand defining an area of overlap in the region of said portion of saidgeometrically periodical structure in the direction of saidcomponents,and output means for extracting said oscillatory electromagnetic waveenergy from said tube.

14. A microwave discharge system adapted to operate as an ultra-highfrequency oscillator within a given frequency band, comprising means forproducing two electron beams having velocity components in mutuallyopposite directions and propagating with a spatial extension such thatthe projection of one of said beams on the other defines a common areaextended substantially in the direction of said components, meansincluding a geometrically periodical structure disposed between saidbeams with-in said common area and essentially preventing propagationtherealong of electromagnetic waves within at least said given frequencyband for generating oscillatory electromagnetic energy by the mutualinteraction of the electric fields of said beams Within said area ofoverlap, and output means for-extracting said oscillatory tureessentially inhibiting propagation therealong of elecf tromagnetic waveswithin at least said given frequency bandand provided with aperturemeans, means for propagating two electron beams of substantial width onopposite sides of said first-mentioned means in diiferent directionswith velocity components thereof in mutually opposite directions anddefining a common area of overlap in said mutually opposite directionsby the projection of one of said beams on the other for generatingoscillatory electromagnetic energy by the effective mutual intermittentinteraction of said two beams through said aperture means, and outputmeans for extracting said oscillatory electromagnetic energy from saidtube.

References Cited in the file of this patent UNITED STATES PATENTS2,636,948 Pierce Apr. 28, 1953 8 Hollenberg Sept..1'5, Pierce- May 10,Pierce Jan. .10, Webber Feb. 14, Hagelbarger et a1. May 15, Walker May15, Huber et al. July 31, Cutler Oct. 22, Diemer July 22, Ashkin et al.Jan. 27, Charles et al. Nov. 3,

FOREIGN PATENTS France July 18, Great Britain Nov. 4, Great Britain Mar.24,

OTHER REFERENCES Traveling Wave Tubes, by J. R. Pierce, pub. 1950 by V.Van Nostrand Co., Inc., New York, page 90.

